The present invention relates to an inductively-coupled radio frequency plasma mass spectrometer for mass analysis with an inductively-coupled radio frequency plasma as an ion source.
Conventionally, an inductively-coupled radio frequency plasma mass spectrometer is more suitable for microanalyses than an inductively-coupled radio frequency plasma emission spectro-analyzer because of its high sensitivity. Further, the former is suitable for analyzing isotope, so that wide applications have been recently developed.
The inductively-coupled radio frequency plasma mass spectrometer comprises an apparatus such that an induction coil is provided through which radio frequency current flows, and where aerosol is introduced into a plasma torch to thereby generate an inductively-coupled radio frequency plasma (referred to as "ICP" hereinbelow). Ions are thereby generated and introduced into a mass spectrometer, so that the mass of the ions can be analyzed.
In the conventional type of the above-descrived mass spectrometer, the energy of the ions developed by the ICP is too high to afford sufficient resolution in the mass spectrometer. FIG. 3(a) shows a graph representing the spectra of the energy of the ions. As shown in FIG. 3(a), the spectra of the energy of the ions is so wide that the ion beam cannot be focused enough by a lens system leading the ion beam to the mass spectrometer, whereby the signal output is relatively low. Further, while the ion taken out of the plasma is introduced into a vacuum chamber containing the mass spectrometer therein via an orifice, the voltage of the plasma is varied so that a pinch discharge is caused between the ICP and the orifice. The orifice may be damaged. A ultra violet ray noise may be caused because of the pinch discharge, so that the accuracy of the mass spectrometer may be influenced. No improved mass spectrometer has yet been presented to resolve the above problems.